In any communications network, it is important to know the physical location of each subscriber within that network. With respect to conventional landline, public switched telephone networks (PSTN), the location of each subscriber in the network is known because the location of the telephone instrument assigned to each subscriber is substantially fixed and thus is known, due to the hard-wire nature of the PSTN system. Each telephone instrument is connected by wires (telephone line) to a central switching facility and is assigned a particular number. The ability of the network to contact the subscriber is limited to the terminus location of the connecting telephone line.
Cellular communications technology provided an alternative to the conventional landline fixed communication network and introduced a widely accessible and practical mobile communications concept. Within a cellular network, each cellular telephone has an assigned number, and an ability to communicate with all telephones within the cellular area, including landline telephones. With the development of cellular networks, however, the need for location supervision of the individual cellular units in a particular network became necessary. Currently, location registration of cellular units is accomplished in one of two ways, as specified in EIA/TIA-553, which is the mobile station-land station compatibility specification for the United States cellular system. In the first location registration system, which is generally referred to as periodic registration, automatic reporting at specific times is provided by the subscriber cellular unit to the central exchange of the cellular network. The subscriber's location is identified to the central exchange as a particular cell site within the overall system. In operation of the first system, the central exchange regularly sends a "current time" value, referred to as REGID, to all mobile cellular units. A stored "wake-up time", referred to as NXTREG, is set in the mobile unit after the occurrence of certain specified events, such as registration, origination access or page response. The wake-up time is set by adding a particular number of steps, referred to as REGINCR, to the current time value (REGID). The mobile unit checks the current time value (REGID) against the wake-up time (NXTREG). In this system mobile cellular units can be required to register at regular intervals over an approximate range from five minutes to five hours.
In the second system, referred to as forced registration, reporting is made by the subscriber unit whenever it crosses a network-defined boundary such as a different system identification (SID) area, a different paging area or other defined boundary. At these crossing points, a transmission is provided to the central exchange identifying the change in location of the subscriber unit.
While either or both of these systems provide location information for the subscriber unit, it is well known that their effectiveness is somewhat limited, because the resulting location of the subscriber unit is specific only to the particular serving cell site within the system. As the cellular industry matures, and smaller and smaller cell sizes become more prevalent, location identification will become more precise, but such increased preciseness will still not be completely satisfactory. Preferably, a cellular network should be able to direct calls to and from a subscriber unit wherever that subscriber unit is located, by any convenient means, including, where appropriate, communication by a landline telephone network. A significant increase in the level of preciseness of identifying the location of a subscriber unit in a cellular network is thus needed.
The network should be able to direct calls to and from a subscriber not only on a location basis, but also be able to deliver a call to the proper terminal. For instance, at a location where both the cellular telephone itself and/or a conventional landline telephone are located, it is important to know to which instrument a particular call should be directed. Additional sophistication may be desired even when the system knows the subscriber's location. For instance, a power-down communication from the cellular unit which is interpreted to mean that communication should occur through the landline network, would not be satisfactory in the situation where the subscriber does not wish to be disturbed.
Accordingly, an apparatus is needed which can be conveniently used with existing cellular networks to provide updated location registration for each subscriber unit within the system, as soon as and as frequently as a change in location of the unit occurs.